Aortic diseases mainly include aortic dissection and aortic aneurysm; the aortic aneurysm is further divided into true aortic aneurysm and false aortic aneurysm. The aortic aneurysm or aortic dissection, with mortality rate higher than 50% within 48 hours and higher than 85% within two weeks after the onset, is a very dangerous disease which has been a serious threat to human health. With the advent of China's aging population trends, the incidence thereof will be constantly rising.
Taking the thoracic aortic dissection as an example, as shown in FIG. 1, an aorta 1 includes an ascending aorta 11 connected to the heart, a descending aorta 12, and an aortic arch 13 between the two; the descending aorta 12 comprises a thoracic aorta 21 and an abdominal aorta (not shown in the figure); the aortic arch 13 has three branch vessels comprising an innominate artery 15, a left common carotid artery 16 and a left subclavian artery 17. Due to the damage of the aortic intima, the high pressure blood flows through a dissection crevasse 18 and rushes into the vessel wall to tear the tunica media, so that the integrated structure of the aortic wall is divided into two parts, and a dissection lumen 20 is formed in a chapped gap between the inner and outer walls of the dissection. In order to distinguish it from the aortic lumen, the dissection lumen 20 is called as a false lumen, whereas the aortic lumen is called a true lumen. The dissection lumen 20 is located at a greater curvature side 19 of the thoracic aorta 21, and may also be formed at a lesser curvature side 22 of the thoracic aorta.
At present, surgical treatments on these diseases mainly refer to traditional open heart surgery and minimally invasive endovascular exclusion surgery. The surgical treatments present great difficulty, are difficult operations, involve long operation time, often result in heavy wounds to patients, and have high mortality rates. Meanwhile, assistive technologies, such as deep hypothermic circulatory arrest, cerebral perfusion, conventional cardiopulmonary bypass, rising and decreasing temperature, cardiovascular anesthesia and etc., are also required. In addition, pipelines in the surgical field are numerous and have complex order and many anastomotic stomas, resulting in prolonging the operation time and correspondingly prolonging the cerebral ischemia time and extracorporeal circulation time, thereby increasing the operative mortality rates and complications (especially cerebral complications).
In the minimally invasive interventional treatment technology using the lumen isolation principle, the covered stent is usually used for isolating the blood flow from the aortic aneurysm or aortic dissection. Aortic covered stents on the current market mainly consist of a metal wire and PET (Polyethylene Terephthalate Resin) membrane or ePTFE (Polytetrafluoroethylene) membrane covered on the metal wire, the metal wire is made into a straight tube-shaped stent frame and covered by the PET membrane or ePTFE membrane. A covered stent in a compressed state is conveyed into the human body through a delivery system with a relatively small luminal diameter under the guidance of a guide wire positioned in advance, accurately released after reaching the position of a diseased vessel with the help of a developing system, and covered on the diseased vessel segment to isolate the lesion and to form a new blood flow channel. For the aortic aneurysm, after losing the blood supply, the blood remained in the tumor cavity is gradually formed into thrombus and muscularized to form vascular tissues, the aneurismal wall in an extended state is constricted due to a negative pressure, and gradually restored to solve the primitive form, thereby achieving the purpose of treating the aortic aneurysm. For the aortic dissection, the aortic dissection crevasse is covered by the covered stent, the thrombus is gradually formed in the false lumen, and the negative pressure is gradually decreased, thereby achieving the purpose of treating the aortic dissection.
At present, the thoracic aortic covered stent (hereinafter referred to as stent) includes two kinds such as one with a bare stent segment at a proximal end and the other without a bare stent segment at the proximal end, wherein the bare stent segment here refers to a metal wire tube-shaped part not covered by a membrane. In the industry, the proximal end and the distal end of the stent are defined according to the blood flow direction, and the blood flows to the distal end from the proximal end of the stent. The bare stent segment at the proximal end may lengthen an anchoring region at the proximal end of the stent without blocking the branch vessels on the aortic arch, and will improve the apposition performance of the covered proximal end of the stent to the wall. Therefore, the stent has better adaptability for patients with a dissection crevasse in the thoracic aorta relatively close to the branch vessels on the aortic arch, or with relatively short thoracic aortic aneurysm neck.
In the existing stent, the bare stent segment is usually fixed to the proximal end of the membrane by suturing, so the bare stent segment and the covered stent segment are in flexible connection, in order to ensure the overall flexibility after the stent is implanted. However, during the endovascular release process of the stent, the stent is pushed by a deployer at the distal end of the stent, and gradually released from the proximal end to the distal end; due to the flexible connection between the bare stent segment and the covered stent segment, the pushing force will probably cause the metal wire in the bare stent segment to overturn towards the vessel wall and to contact with the vessel wall, so that the proximal end of the covered stent segment may not be securely apposed to the wall, thereby resulting in the “turnover effect. Once there is a “turnover” effect”, not only the metal wire overturned in the bare stent segment will damage the blood vessel, but also I type endoleak is easily generated between the stent and the blood vessel, namely due to the proximal end of the stent and the blood vessel being not completely enclosed, the blood continuously flows into the aortic aneurysm or the aortic dissection, thereby resulting in continually growing of the aneurysm cavity or the dissection cavity, and leading to the treatment failure and ultimately leading to serious consequences such as rupture.